Agency

Build calculators that bring in leads for agencies and accountants

Build one-page calculators where an agency's or accounting firm's prospects enter their own numbers and get an answer, such as the ad return they need to break even or how much they would take home as an S-corp instead of a sole proprietor. Each page shows the firm's case studies next to the result and collects the visitor's email, and the firm pays you to build it.

The hard part: getting the math right for each industry so the firm trusts it, and finding firms willing to pay for a page they could ask their own team to build.

Setup 2 daysRuns $20/moYour time A few hours a weekNeeds ClaudeVercelAirtableStripe

Who pays

Ecommerce agencies, accounting firms, and cold email agencies pay you to build a calculator page that brings them new prospects. Our suggestion is a flat fee for each calculator plus an optional small monthly fee for hosting and changes, charged through Stripe Payment Links. This pricing is a suggestion. The sources show calculators being built and used to bring in leads, not anyone's revenue from selling them to firms.

How to build it

  1. Pick one industry and calculator

    Start with one kind of firm, such as ecommerce agencies, and one calculator its prospects care about, such as a break-even ad return calculator (ad spend, average order value, and product cost in, minimum return out). Ask a friendly firm which numbers their prospects always ask about.

  2. Build the page with AI

    Ask Claude, or Claude Code, to write a single HTML page with the input boxes, the formula, and a clear result. Test it against a spreadsheet version of the same math before showing anyone.

  3. Add proof next to the result

    Put the firm's case studies, testimonials, or client videos right beside the result so the visitor sees how the firm helps with the number they just saw.

  4. Collect emails into a list

    Add an email box that unlocks the full breakdown. Send each sign-up and the numbers the visitor entered to an Airtable base the firm can see.

  5. Host it and hand it over

    Publish the page on Vercel under the firm's own domain or embed it on their site. Charge the build fee and any monthly plan through Stripe Payment Links.

  6. Reuse the template for new firms

    Keep each calculator as a template so the next agency or accounting firm only needs new branding, case studies, and small changes to the math.

Sources on X

  • termsheetinator · May 10, 2026

    The poster lists simple HTML calculator pages as lead magnets for different kinds of firms, including a ROAS breakeven calculator for ecom agencies (ad spend, AOV, COGS in, minimum ROAS to profit out), a sole prop vs. S-corp vs. C-corp take-home comparison for accountants, and a campaign ROI calculator for cold email agencies. The poster says each one should have embedded case studies, testimonials, and client videos.

  • SiteTrail · Oct 10, 2026

    SiteTrail writes that most accounting firms know a client's margin to the penny but shrug when asked what they can afford to pay to win that client. The poster says they wrote up the math and built a free app that does it.

  • ArnaudBelingaCX · May 17, 2026

    ArnaudBelingaCX says they built a Cold Email ROI Calculator because most online versions skip the real costs of the sending setup and the pipeline that comes from prospects who check you out later. The poster offered it to anyone who replied "CALCULATOR", using the calculator itself to collect leads.

Ideas are curated from public posts and untested by us. Read the full note.